The invention relates to a data compression apparatus for data compressing an audio signal, to a data compression method, a transmitter including the data compression apparatus, a recording apparatus including the data compression apparatus, a record carrier having the data compressed audio signal recorded on it in a track of the record carrier, to a data expansion apparatus for data expanding a data compressed audio signal, to a data expansion method, a receiver including the data expansion apparatus and to a reproducing apparatus including the data expansion apparatus.
Data compression on an audio signal is well known in the art. Reference is made in this respect to EP-A 402,973, document D1 herein list of related documents. The document describes a subband coder, in which an audio signal is A/D converted with a specific sampling frequency, such as 44.1 kHz, and the resulting samples in the form of eg. 24 bits wide words of the audio signal, are supplied to a subband splitter filter. The subband splitter filter splits the wideband digital audio signal into a plurality of relatively narrow band subband signals. Using a psycho acoustic model, a masked threshold is derived and blocks of samples of the subband signals are subsequently quantised with a specific number of bits per sample for each block of the subband signals, in response to the masked threshold, resulting in a significant data compression of the audio signal to be transmitted. The data compression carried out is based on `throwing away` those components in the audio signal that are inaudible and is thus a lossy compression method. The data compression described in document D1 is a rather intelligent data compression method and requires a substantial number of gates or instructions, when embodiment either in hardware or software respectively, so that it is expensive. Moreover, the subsequent expansion apparatus also requires a substantial number of gates or instructions, when implemented in hardware or software respectively.
Those skilled in the art are hereby referred to the following listed documents:
(D2) "A digital decimating filter for analog-to-digital conversion of hi-fi audio signals", by J. J. van der Kam in Philips Tech. Rev. 42, no. 6/7, April. 1986, pp. 230-8 PA1 (D3) "A higher order topology for interpolative modulators for oversampling A/D converters", by Kirk C. H. Chao et al in IEEE Trans. on Circuits and Systems, Vol. 37, no. 3, March. 1990, pp. 309-18 PA1 (D4) "A method for the construction of minimum-redundancy codes", by D. A. Huffman in Proc. of the IRE, Vol. 40(10), September 1952. PA1 (D5) "An introduction to arithmetic coding" by G. G. Langdon, IBM J. Res. Develop., Vol. 28(2), March 1984. PA1 (D6) "A universal algorithm for sequential data compression" by J. Ziv et al, IEEE Trans. on Inform. Theory, Vol. IT-23, 1977. PA1 input apparatus for receiving the audio signal, PA1 conversion apparatus for carrying out a conversion on the audio signal so as to obtain a 1-bit bitstream signal, the conversion apparatus comprising sigma-delta modulator apparatus, PA1 lossless coding apparatus for carrying out a substantially lossless data compression step on the bitstream signal so as to obtain a data compressed bitstream signal, and PA1 output apparatus for supplying the data compressed bitstream signal. More specifically, when the audio signal is an analog audio signal, the conversion apparatus is in the form of A/D conversion apparatus for carrying out a 1-bit A/D conversion on the analog audio signal so as to obtain the bitstream signal.
The above citations and tho sin the list of related documents below are hereby incorporated in whole by reference.